While many compounds have been proposed for use as binders in thermally developable, light-sensitive materials, hydrophobic poly(vinyl butyral) is used most commonly. Techniques of using water-soluble binders are also known; thermally developable, light-sensitive materials using gelatin as the binder are shown in Japanese Patent Application (OPI) Nos. 52626/1974 and 116144/1978 (the symbol OPI as used herein means an unexamined published Japanese Patent Application), U.S. Pat. No. 4,168,980, Japanese Patent Publication Nos. 26582/1969, 12700/1970 and 18416/1970, whereas the use of poly(vinyl alcohol) as a binder is shown in Japanese Patent Application (OPI) No. 151138/1975 and Research Disclosure (hereunder referred to as RD) No. 17707. Japanese Patent Application (OPI) No. 28737/1983 shows the use of water-soluble poly(vinyl butyral) as a binder.
One of the major reasons for using these water-soluble binders is to provide a higher sensitivity through the use of a conventional silver halide emulsion Gelatin is considered to be the most advantageous binder because of its setting properties that can be effectively used during its manufacture and application stages. However, gelatin per se has no thermoplasticity and the thermal developability of the light-sensitive material that uses only gelatin as a binder is quite low. In order to solve this problem, techniques of using gelatin in admixture with a polar organic compound such as dimethylurea or acetamide have been proposed in U.S. Pat. Nos. 3,438,776 and 3,667,959, as well as Japanese Patent Application (OPI) Nos. 137321/1977 and 116144/1978. A similar technique is shown in Japanese Patent Application No. 82064/1982 filed by the applicant of subject application. Other references not mentioned here show the technique of using gelatin in combination with other water-soluble polymers.
Thermally developable, color light-sensitive materials are shown in many references. For example, U.S. Pat. Nos. 3,531,286, 3,761,270, 3,764,328, RD Nos. 15108, 15127, 12044 and 16479 show thermally developable, light-sensitive materials of the type that contains both a photographic coupler and a color developing agent; U.S. Pat. No. 3,180,731, RD Nos. 13443 and 14347 show products containing a leuco dye; U.S. Pat. No. 4,235,957, RD Nos. 14433, 14448, 15227, 15776, 18137 and 19419 show products using the silver dye bleaching method; and U.S. Pat. Nos. 4,124,398, 4,124,387 and 4,123,273 show the method of thermally bleaching a heat developable, light-sensitive material.
Thermally developable, color light-sensitive materials of the type that produces a color image by transferring a diffusible dye which has been released or formed by thermal development are shown in Japanese Patent Application (OPI) Nos. 179840/1972, 186744/1982, 19845/1982, 207250/1982 and 0551/1983. Japanese Patent Application No. 129516/1983 shows a thermally developable, color light-sensitive material which contains a compound capable of forming a heat-transferable dye.
For various reasons such as the need for providing a higher sensitivity and for ensuring good process stability, it is advantageous to use silver halide-gelatin emulsions. However, as already pointed out, systems using gelatin as the sole binder do not have high developability, and combining gelatin with a polar organic compound such as dimethylurea or acetamide has been proposed for providing a higher developability. Although some improvement in developability is achieved by this method, the result is not completely satisfactory in respect of the balance between development, coupling reaction (dye formation or its release) and the heat transfer of the dye released or formed.
It is known that the results of development, coupling reaction and the heat transfer of a released or formed dye onto an image-receiving layer can be greatly improved by using a water-soluble binder made of only a thermoplastic polymer such as poly(vinyl alcohol) or water-miscible poly(vinyl butyral) on the condition that silver halide is prepared within the same polymer. Therefore, attempts have been made to mix gelatin with a water-soluble polymer such as poly(vinyl alcohol) or water-miscible poly(vinyl butyral). More specifically, a silver halide-gelatin emulsion is simply mixed with poly(vinyl alcohol) or other water-soluble polymers in an attempt at providing a higher sensitivity without sacrificing the developability and the efficiency of coupling reaction, or at enabling the simultaneous application of multi-layers by making the most of the setting properties of gelatin. However, the desired improvement in the developability and the efficiency of coupling reaction cannot be obtained by simply mixing the water-soluble polymer with gelatin. Poly(vinyl alcohol) and water-soluble poly(vinyl butyral) are generally low in their miscibility with gelatin and have a tendency to form "islands" (aggregates) during mixing with gelatin or when they are being dried. Because of this tendency, the mere mixing of water-soluble polymers with gelatin is not highly effective in providing improved developability and a better efficiency of coupling reaction, and the "islands" prevent the formation of a transferred dye image of good quality.